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Controlling the ratio of amplification factors between linear amplifiersControlling the ratio of amplification factors between linear amplifiers description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070188237, Controlling the ratio of amplification factors between linear amplifiers. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is related to French Patent Application No. 0513489, filed Dec. 30, 2005, entitled "METHOD FOR CONTROLLING THE RATIO OF THE AMPLIFICATION FACTORS OF TWO LINEAR AMPLIFIERS, AND DEVICE FOR SAME". French Patent Application No. 0513489 is assigned to the assignee of the present application and is hereby incorporated by reference into the present disclosure as if fully set forth herein. The present application hereby claims priority under 35 U.S.C. .sctn.119(a) to French Patent Application No. 0513489. TECHNICAL FIELD [0002] The present disclosure relates to amplifiers and, notably, to the control of the ratio between the amplification factors of at least two amplifiers with controllable amplification factors such as, for example, linear amplifiers. BACKGROUND [0003] Conventionally, a receiver unit includes various filters whose cut-off frequency must be very precisely fixed. However, by reason of temperature variations or of the variations, for example, in the power supply voltage, the parameters of the filters used exhibit very wide variations typically between 40% and 50%. [0004] In order to limit these variations, the filter cut-off frequency is controlled by a control signal delivered by another system called a master system. This conventional filter structure is described, for example, in the article `Integrated Continuous-Time Filter Design--An Overview`, Yannis Tsividis, IEEE Journal of Solid-State Circuits, vol. 29, no. 3, Mar. 1997, pp. 166-176. The master system may include for example, a phase-locked loop operating according to a stable reference frequency delivered by an external component such as, for example, a quartz oscillator. The master system includes linear amplifiers that are identical to (or possibly homothetic with) those incorporated into the filter, and with an amplification factor that is internally controlled by the same signal used for controlling the cut-off frequency of the filter. [0005] This control of the master/slave type (the slave being the filter) typically allows a precision of around 5%. Furthermore, in order to make the filter operate over various frequency ranges, a divider or a multiplier by N may be used between the control signal output from the master system and the control signal of the filter, if the relationship between the amplification factor of the amplifiers incorporated in the filter and its control quantity is perfectly proportional. Thus, the ratio N may be introduced between the amplification factor of the master system amplifiers and the amplification factor of the amplifiers of the filter. [0006] Owing to the relationship between the amplification factor and the frequency (detailed herein below), the cut-off frequency of the latter is varied as a function of the oscillation frequency of the master system, in the same ratio N. Accordingly, if V denotes the control signal output from the master system, k is the amplification factor of the ideal amplifiers used in the filter and the master system, and by the relationship k=A*V, where A is the coefficient linking the control signal, then Equation 1 below results. f osc = A V k 2 .times. .pi. .times. .times. C .times. .times. and .times. .times. fc = A V k N 2 .times. .pi. .times. .times. C ( Eqn . .times. 1 ) [0007] In Equation 1, f.sub.osc is the master system oscillation frequency, f.sub.c the filter cut-off frequency and C a reference capacitance value for the device in question (master system or filter to be controlled). Using these relationships, Equation 2 results. f.sub.c=f.sub.osc/N (Eqn. 2) [0008] In other words, by controlling and adjusting the amplification factor k of the amplifiers incorporated into the filter by means of a control signal such as that described hereinabove, a ratio of N is established between the amplification factors of the master system and of the filter, and hence the oscillation frequency of the master system and the cut-off frequency of the filter. [0009] However, the relationship of proportionality between the value of the control signal of the amplifier and its actual amplification factor is never perfect. For example, non-linearities in the control of the amplifier always exist and thus lead to the impossibility of using directly the principle stated hereinabove between the theoretical relationship of proportionality and that observed between the oscillation frequency of the master system and the cut-off frequency of the filter, in this example. [0010] There is therefore a need for a device that is capable of establishing a ration N between two amplification factors, and more particularly, a device capable of establishing two frequencies which are independent of the non-linearity phenomena in the control of the amplifiers. SUMMARY [0011] The present disclosure provides a device capable of establishing a ratio N between at least two amplification factors, and consequently two frequencies, which is independent of the non-linearity phenomena in the control of the amplifiers. The present disclosure also provides a device that allows a filter cut-off frequency to be controlled by means of a stable external signal, in particular when a division or multiplication ratio is introduced between the filter cut-off frequency and the external frequency. [0012] In one embodiment, the present disclosure provides an electronic device having a main circuit. The main circuit includes at least two main linear amplifiers each having a respective amplification factor and each respectively controllable by two main control signals. Each of the main linear amplifiers can respectively receive two input signals and deliver two output signals, the levels of the two input signals being in a ratio N. The main circuit also includes a controller to adjust the value of at least one of the two main control signals in such a manner as to equalize the output signals, the two amplification factors then being in the same ratio N. [0013] In another embodiment, the present disclosure provides a method of controlling the ratio of amplification factors of controllable linear amplifiers. The method includes adjusting N to a desired value. N is the ratio between the respective amplification factors of two main linear amplifiers that are controllable by two main control signals. The adjustment is accomplished by receiving two input signals and the delivery of two output signals by the main amplifiers, where the levels of the two input signals being in a ratio of N. The adjustment also includes controlling one of the two main control signals so as to equalize the output signals, where now the two amplification factors are in the same ratio N. [0014] In still another embodiment, the present disclosure provides a main circuit with a differential architecture. Thus, the input and output signals are of differential quantities. The main circuit includes at least two main linear amplifiers each having a respective amplification factor and each respectively controllable by two main control signals. Each of the main linear amplifiers can respectively receive two input signals and deliver two output signals, the levels of the two input signals being in a ratio N. The main circuit also includes a controller to adjust the value of at least one of the two main control signals in such a manner as to equalize the output signals, the two amplification factors then being in the same ratio N. The controller includes a feedback circuit to control the value of one of the control signals to the difference between the two output signals. [0015] Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions and claims. BRIEF DESCRIPTION OF THE DRAWINGS [0016] For a more complete understanding of this disclosure and its features, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: [0017] FIG. 1 describes schematically an embodiment of a main circuit according to the present disclosure; [0018] FIG. 2 describes in more detail an embodiment of a main circuit according to the present disclosure; [0019] FIG. 3 describes more particularly an example of a part of a linear amplifier incorporated in a device, according to the present disclosure; Continue reading about Controlling the ratio of amplification factors between linear amplifiers... 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